Mobile communication devices, such as cell phones, personal digital assistants (PDAs) and laptop computers, are very widespread, and have become an essential part of modern life. Such devices generally communicate via voice or instant messages. Most instant messages use the Short Message Service (SMS) protocol for sending text messages, but other messages, such as Multimedia Messaging Service (MMS) messages, are also very much in use. According to http://en.wikipedia.org/wiki/Short message service, currently 2.4 billion active users around the world, which is roughly 74% of all mobile phone subscribers, send and receive text messages on their phones.
The SMS Point-to-Point protocol (SMS-PP) is defined in GSM Recommendation 3.40*. Messages are sent to a Short Message Service Center (SMSC), which provides store-and-forward functionality, for transmission to recipients. SMSC supports mobile-terminated (MT) functionality, for messages sent to a mobile handset, and supports mobile-originating (MO) functionality, for messages sent from a mobile handset.
Transmission of messages from the SMSC to a recipient mobile handset is in conformance with the Mobile Application Part (MAP) of the SS7 protocol. In particular, messages are sent using the MAP ForwardSM operations, which limits the length of messages to 140 octets; i.e., 1,120 bits. Routing data and other metadata is added to the message, beyond the 1,120 bit limit.
SMS messaging supports two modes; namely, text and data. For text mode, the message uses the default GSM 7-bit alphabet for regular text messages, supporting 70 characters; and uses 16-bit UCS-2 character encoding for languages such as Arabic, Chinese, Korean, Japanese, and for Cyrillic alphabet languages such as Russian, supporting 160 characters. For data mode, the message uses 8-bit characters and supports 140 characters. Data mode supports inter alia the following services.                WAP Push, which is an encoded message that includes a link to a WAP or WWW address. WAP Push enables WAP content to be pushed to a mobile handset with minimal user intervention. A Push Proxy Gateway (PPG) processes WAP Pushes and delivers them over an IP or SMS bearer.        OTA Settings, which relate to setup of new services, such as GPRS, MMS and Instant Messaging, for a subscriber of a mobile phone network.        MMS Notification, which indicates when a new MMS messages has been received on the Multimedia Messaging Service Center (MMSC). Depending on the phone settings, the message may be automatically downloaded from the MMSC, if a GPRS or UMTS connection is available.        Push E-mail, for receiving e-mail messages on a mobile handset.        
A drawback with SMS messaging is the relatively high cost. According to a recent study the University of Leicester, http://www.spacemart.com/reports/SMS Texting Costs Are Out of This World 999.html, sending text messages by mobile phones is far more expensive than downloading data from the Hubble Space Telescope. Operators charge subscribers per SMS text message, or offer SMS plans, such as unlimited SMS texting for a fixed monthly rate. For some plans, pricing is different for messages sent within a network or within a predefined group, than for messages outside of the network or group.
Costs for instant messaging generally comprise a significant portion of subscribers' monthly fees. The expense is often excessive, since many subscribers perceive sending of text messages as being inexpensive, and much cheaper than phone calls.
A factor that contributes to excessive messaging expenses is the distribution of messages to a group of friends. Often a subscriber broadcasts messages to his friends notifying them of events, or about his status. E.g., if the friends wish to go to a movie together, the subscriber may send a message notifying them of the time and place. Messaging applications, such as 3jam developed by 3jam, Inc, of San Francisco, Calif., and Send'm developed by SEND-M, Ltd, of Or Yehuda, Israel, enable users to send a message to a group of friends. Generally, each member of the group knows which group members are on the mailing list, and may reply to some or all of the group members.
A disadvantage of sending of group messages using conventional technology is that the subscriber who initiates the message must bear the entire cost of the communication. Another disadvantage of sending of group messages using conventional technology is that the initiator of the message does not know whether the recipients actually received the message.